In recent years, multimedia services which provide services regarding information transmissions and information provision by radio are becoming active, and a number of wireless apparatuses have been developed and put into commercial use. The services are being diversified to the telephone, television, LAN (Local Area Network) and the like year after year. To enjoy all of the services, the user has to have wireless apparatuses corresponding to the individual services.
To improve the convenience for the user to enjoy such services, movement of providing the multimedia services any time, any where without making the user aware of the existence of the media, that is, in a ubiquitous manner has started, and a so-called multi-mode apparatus realizing a plurality of information transmission services by itself is realized.
Since normal wireless ubiquitous information transmission uses electromagnetic waves as a medium, in the same service area, by using one frequency for one kind of service, a plurality of services are provided to the users. Therefore, the multimedia apparatus has the function of transmitting/receiving electromagnetic waves of a plurality of frequencies.
A conventional multimedia apparatus employs, for example, a method of preparing a plurality of antennas each of a single mode corresponding to one frequency and mounting the antennas on a single wireless apparatus. According to the method, the single-mode antennas have to be mounted apart from each other by a distance of about a wavelength so as to operate independently. Since frequencies of electromagnetic waves used for services regarding normal ubiquitous information transmission are limited to a few hundreds MHz to a few GHz due to regulation of propagation characteristics in a free space, the distance between neighboring antennas is tens cm to a few meters. Therefore, the dimensions of the apparatus become large, and portability for the user is not satisfied. Since antennas having sensitivities to different frequencies are disposed with sufficient distance, there is the problem of increase in dimensions of the apparatus.
There is another antenna having sensitivities to a plurality of frequency bands. For example, a two-frequency antenna in which one end of a loop antenna or an aerial member is coupled to an RF circuit handling one frequency and the other end is coupled to an RF circuit handling a different frequency is disclosed in Japanese Patent Laid-Open Nos. S61(1986)-265905 and H1(1989)-158805.
In the two-frequency antenna disclosed in Japanese Patent Laid-Open No. S61(1986)-265905, a first resonant circuit is connected to one of terminals of a loop antenna as a radiator and a second resonant circuit is connected to the other terminal. A configuration is employed such that the one terminal resonates at a transmitting frequency and the other terminal resonates at a receiving frequency, a transmitting circuit is connected to the one terminal (transmitting output terminal), and a receiving circuit is connected to the other terminal (receiving input terminal).
On the other hand, the two-frequency antenna disclosed in Japanese Patent Laid-Open No. H1-158805 employs a configuration such that a first resonant circuit which resonates at a transmitting frequency and is connected between one of terminals of an aerial member as a radiator and a transmitting output terminal has a high impedance to a receiving frequency, and the aerial member is disconnected from the transmission output terminal. A second resonant circuit which resonates at a receiving frequency and is connected between the other terminal of the aerial member and a receiving input terminal has a high impedance to the transmitting frequency, and the aerial member is disconnected from the receiving input terminal.